Clean the mushrooms and slice half of them. Finely chop the other half. Heat the olive oil in a large saucepan set over medium-high heat and add the butter. When the foam subsides, add the onion, garlic, and both sliced and chopped mushrooms. Reduce the heat slightly and saute until the moisture evaporates and the mushrooms begin to turn golden.

Add the flour and cook, stirring to coat the mushrooms, for another minute. Add the stock and beans and bring to a simmer. Reduce the heat to low and cook for about 15 minutes.

Turn off the heat and stir in the cream. Season with salt and pepper and serve immediately.